Knockdown of Beclin 1 inhibits vitamin K3‑induced autophagy, but promotes apoptosis of human hepatoma SMMC-7721 cells

Abstract

The aim of the present study was to investigate the effects of Beclin 1 knockdown on spontaneous and vitamin K3 (VK3)-regulated autophagy, survival and apoptosis in human hepatocarcinoma SMMC-7721 cells, and to explore the potential mechanisms underlying the action of Beclin 1 knockdown in the processes of autophagy and apoptosis. A recombinant plasmid-expressing small interfering RNA (siRNA) targeting Beclin 1 mRNA was constructed and introduced into SMMC-7721 cells. The expression of Beclin 1 was determined by reverse transcription-polymerase chain reaction and Western blotting. Subsequently, the impact of Beclin 1 knockdown on spontaneous and VK3-induced autophagy, survival and apoptosis was determined. The expression of cyclin D1, cyclin-dependent kinase 4 (CDK4), Bcl-2, Bcl-xL and the activation of caspase-3 were examined by Western blotting. Transfection with the plasmid for Beclin 1 siRNA expression dramatically down-regulated Beclin 1 expression in SMMC-7721 cells. The knockdown of Beclin 1 expression significantly inhibited spontaneous and VK3-induced autophagy, but did not affect spontaneous proliferation and apoptosis in SMMC-7721 cells in vitro. By contrast, the silencing of Beclin 1 expression significantly enhanced the inhibition of survival and proliferation by VK3, and promoted VK3-induced apoptosis by significantly down-regulating cyclin D1, CDK4, Bcl-2 and Bcl-xL expression and enhancing caspase-3 activation in SMMC-7721 cells in vitro. Our data indicate that Beclin 1 is a positive regulator of autophagy, but a negative regulator of VK3-induced apoptosis in human hepatoma cells.